title: A tetrapyrrole-regulated ubiquitin ligase controls algal nuclear DNA replication.
abstract: In plant cells, organelle DNA replication (ODR) is coordinated with nuclear DNA replication (NDR), with ODR preceding NDR during cell cycle progression. We previously showed that the occurrence of ODR is signalled by a tetrapyrrole compound, most likely Mg-protoporphyrin IX (Mg-ProtoIX), resulting in the activation of cyclin-dependent kinase A (CDKA) and consequent initiation of NDR (refs 1, 2, 3). Here we identify an F-box protein of SCF-type E3 ubiquitin ligase (Fbx3) in the red alga Cyanidioschyzon merolae, which inhibits CDKA by ubiquitylating the relevant cyclin and inducing its degradation. Mg-ProtoIX binds to Fbx3 and inhibits cyclin ubiquitylation. Thus, these observations indicate that Fbx3 serves as the receptor for the plastid-to-nucleus retrograde signal Mg-ProtoIX and thereby contributes to a checkpoint mechanism ensuring coordination of ODR and NDR.
authors.affiliation: Graduate School of Horticulture, Chiba University, 648 Matsudo, Matsudo, Chiba 271-8510, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Kobayashi
authors.forename: Sousuke
authors.initials: S
authors.lastname: Imamura
authors.forename: Mitsumasa
authors.initials: M
authors.lastname: Hanaoka
authors.forename: Kan
authors.initials: K
authors.lastname: Tanaka
mesh_terms: D018844:Cyclin-Dependent Kinases / Q000235:genetics / Q000378:metabolism; D016213:Cyclins / Q000235:genetics / Q000378:metabolism; D004261:DNA Replication; D044783:F-Box Proteins / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D000461:Rhodophyta / Q000201:enzymology* / Q000235:genetics*; D045725:Tetrapyrroles / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: D016213:Cyclins; D044783:F-Box Proteins; D011993:Recombinant Fusion Proteins; D045725:Tetrapyrroles; D018844:Cyclin-Dependent Kinases